Preeclampsia (PE) is a pregnancy-specific disease that accounts for significant morbidity and 50-76,000 maternal deaths annually worldwide. Fifteen percent of all US preterm births result from PE, accounting for significant neonatal morbidity and mortality. The immediate US health care costs attributable to PE are estimated at $7 billion per year. PE pathogenesis is thought to begin in the first half of pregnancy with impaired interstitial and endovascular invasion of cytotrophoblasts (CTBs) into the maternal tissue. We recently examined the gene expression profile of the placental basal plate, the region of CTB invasion, in pregnancies complicated by PE, identifying 55 genes that are differentially expressed in PE compared to controls including over 40 novel targets. Our long-range goal is to determine whether these differentially expressed genes play key roles in CTB biology, specifically their role in interstitial and endovascular invasion and their contribution to the early stages of PE. For this proposal, we focus the roles of on two of the differentially expressed genes- leptin and Siglec-6 (sialic acid binding Ig like lectin 6) - in trophoblast invasion. Siglec-6 was originally cloned as a leptin binding protein (OB-BP1) with an intracellular tail containing a conserved immunoreceptor tyrosine-based inhibitory motif (ITIM) and an ITIM-like motif, suggesting that Siglec-6 has signaling potential. While the B lymphocytes of all studied primates express Siglec-6, only human placenta expresses Siglec-6, which is intriguing given PE is a human-specific disease dependent upon the placenta. Interestingly, the canonical leptin receptors (ObR) were not differentially expressed in our PE microarray data suggesting that Siglec-6 may serve as the critical leptin receptor in PE. Additionally, we have established that leptin can promote human CTB invasion in vitro and that Siglec-6 expression can abrogate this effect in CTB cell lines. These observations lead to our overall hypothesis that overexpression of Siglec-6 plays a role in PE pathogenesis by functioning as an inhibitory leptin receptor to impair CTB invasion. In this proposal we will test the hypothesis that Siglec-6 overexpression inhibits leptin promotion of CTB differentiation and invasion by altering ObR signaling by answering the following questions: Aim 1. Does Siglec-6 inhibit leptin promotion of human CTB invasion? Aim 2: Are the ObR signaling pathways critical for human CTB invasion modified by Siglec-6 expression? Aim 3: What downstream targets of ObR signaling are altered by Siglec-6 expression during CTB differentiation and invasion? Discovering how the PE-associated molecules leptin and Siglec-6 regulate CTB invasion will determine their potential role in early PE pathogenesis. Ultimately, understanding the complex pathways that regulate trophoblast invasion will provide the insights needed to develop novel preventative, diagnostic and/or treatment strategies geared at the cause rather than the consequences of this serious pregnancy disease, thereby improving the health of the 8 million woman-infant pairs annually afflicted by PE.